(1) Field of the Invention
The present invention relates to an idle speed control apparatus that controls an idle speed of an internal combustion engine according to an operating state of the engine. In particular, the present invention relates to an idle speed control apparatus that controls an idle speed of an internal combustion engine according to an ignition timing controlled for promoting the warm-up.
(2) Description of the Related Art
An internal combustion engine is required to stabilize its idling operation when it is cold started. The internal combustion engine is also required to promote the warm-up so as to promptly activate a catalyst and ensure desired exhaust gas purifying performance.
Therefore, to stabilize the idling operation of the internal combustion engine in a cold mode, the target idle speed is set to a higher speed than normal. Then, the ignition timing of the internal combustion engine is corrected to be later than the normal ignition timing to thereby increase the exhaust temperature. At the same time, the intake air quantity of the internal combustion engine is increased to suppress the reduction of torque produced by the internal combustion engine with the retard of the ignition timing.
For example, a conventional idle speed control apparatus for an internal combustion engine shown in FIG. 14 is constructed such that, during a warm-up, the angle θs of an electronically controlled throttle valve (ETV) is switched at a time point t1 to a warm-up target initial angle θ1. The initial angle θs1 is corrected with age. The intake air quantity Qa and the engine speed Ne are increased and decreased according to variations in the throttle valve θs. At the initial stage of starting, the engine speed Ne overshoots a target idle speed Ne1. Then, the engine speed Ne starts coming closer to the target idle speed Ne1 corresponding to the intake air quantity Qa and the ignition timing IGT.
In this case, in response to a command indicative of the ETV angle θs, the ETV is open-loop controlled to maintain the angle θs as shown in FIG. 14. In response to a command indicative of the ignition timing IGT, an igniting device is feedback-controlled to maintain the ignition timing IGT as shown in FIG. 14. This causes the engine speed Ne to come closer to the target idle speed Ne1, and a variation in the engine speed Ne is corrected.
It should be noted that the internal combustion engine is switched from the warm-up state to steady state at a warm-up completion time point t2. On this occasion, the ETV angle θs is switched to a steady state angle θsn, and the ignition timing IGT is also switched step by step to steady state ignition timing IGT n, so that the engine speed Ne is switched with age to a steady state target idle speed Nen.
According to a prior art disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 10-299631, when an internal combustion engine is idling, the ignition timing is retarded to increase the exhaust gas temperature so as to promptly secure desired purifying performance of a catalytic device. According to this prior art, the reduction of torque produced by the internal combustion engine and the variation of the engine speed accompanied by the retard of the ignition timing are suppressed by increasing the intake air quantity while retarding the ignition timing.
Incidentally, in the case of an electronically controlled throttle valve used in an idle speed control apparatus for an internal combustion engine, the intake air quantity Qa is likely to deviate due to aging changes of the throttle valve or variations among products.
However, the conventional idle speed control apparatus for the internal combustion engine shown in FIG. 14 and the idle speed control apparatus for the internal combustion engine disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 10-299631 open-loop control the intake air quantity.
For this reason, particularly in the case where the intake air quantity Qa is deviated by Δq to smaller values (refer to a broken line in FIG. 14), the target ignition timing IGT is displaced by a deviation ΔIGT toward earlier timing (refer to a broken line) even if the target idle speed Ne is feedback-controlled by correcting the target ignition timing IGT. In this case, the advancement of the target ignition timing IGT has a deficiency equivalent to the deviation ΔIGT, and this leads to insufficient increase of the exhaust gas temperature. As a result, the activation of a catalyst is delayed to increase the total amount of exhaust gases emitted from a vehicle. This problem is desired to be solved.
It is therefore an object of the present invention to provide an idle speed control apparatus for an internal combustion engine, which feedback-controls the intake air quantity and the ignition timing to respective target values during warm-up, thus preventing the exhaust gas temperature from being increased insufficiently due to a deficiency in retard angle, and to prevent the activation of a catalytic converter from being delayed, even if there is a deviation in the angle of the throttle valve due to aging changes of the throttle valve or variations among products.